Wegovy vs. Mounjaro: Mechanism, 72-Week Weight Loss & Side Effects Compared

Key Takeaways

Wegovy (semaglutide) activates GLP-1 receptors alone, whereas Mounjaro (tirzepatide) activates both GIP and GLP-1 receptors for dual metabolic and appetite signaling.
In the 2025 head-to-head SURMOUNT-5 trial (72 weeks), Mounjaro 15mg achieved 21.6% average weight loss versus 15.4% with standard Wegovy 2.4mg — while the newer Wegovy 7.2mg dose reached 19%–21% in STEP UP.
Overall gastrointestinal side-effect rates are similar (77%–79%), though Mounjaro showed slightly lower treatment discontinuation due to adverse events (6% vs. 8%).
Wegovy holds dedicated cardiovascular risk-reduction labeling (SELECT trial), while Mounjaro often excels in patients with concurrent insulin resistance or type 2 diabetes.

Wegovy (semaglutide) and Mounjaro (tirzepatide) are the two leading once-weekly injectable treatments transforming medical weight care. While both use pre-filled pens and 4-week titration schedules, they act on distinct gut-hormone combinations and deliver nuanced clinical profiles.

Head-to-Head Comparison: Wegovy vs. Mounjaro

Clinical Metric	Wegovy (Semaglutide)	Mounjaro (Tirzepatide)
Hormone receptors targeted	Single agonist: GLP-1	Dual agonist: GLP-1 + GIP
Dosing frequency	Once weekly injection (or daily 25mg oral pill)	Once weekly injection
72-week weight loss (SURMOUNT-5)	15.4% mean loss (at 2.4mg)	21.6% mean loss (at 15mg)
High-dose Wegovy 7.2mg (STEP UP)	19%–21% mean loss	20%–22.5% mean loss (SURMOUNT-1, 15mg)
Any GI side effect	~79% (nausea 17–22%, vomiting ~21%)	~77% (nausea 17–22%, vomiting ~15%)
Stopped due to side effects	~8%	~6%
Cardiovascular indication	Proven MACE reduction in established CVD	Strong cardiometabolic & sleep-apnea improvements

Why Dual GIP + GLP-1 Signaling Matters

While GLP-1 slows gastric emptying and signals fullness in the hypothalamus, GIP (glucose-dependent insulinotropic polypeptide) additionally improves adipose-tissue lipid handling, enhances insulin sensitivity, and appears to buffer central nausea pathways slightly — helping explain why tirzepatide achieved greater average weight reduction with marginally fewer discontinuations in the 2025 SURMOUNT-5 trial. Meanwhile, Novo Nordisk’s higher-strength 7.2mg Wegovy pen narrows that gap substantially for patients who respond well to semaglutide.

Can You Switch Between Them?

Yes. Under clinician supervision, patients who plateau or experience persistent side effects on one medication typically complete a 7-day washout after their final weekly pen before starting the alternative on a prescriber-selected titration step (see our Wegovy-to-Mounjaro switching guide). Both medications are contraindicated in pregnancy and in individuals with personal or family history of medullary thyroid carcinoma or MEN2.

References

Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025.
Wharton S, et al. Once-weekly semaglutide 7.2 mg in adults with obesity (STEP UP). Lancet Diabetes Endocrinol. 2025.
Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205–216.

Medical Editorial Review: Reviewed by the Amble Clinical Editorial Team. This article is for educational purposes only and does not replace an individualized consultation with a licensed healthcare professional.